Rock drill bit



Dec. 29, 1964 VAGINS ETAL 7 3,163,246

United States Patent Or 3,163,246 ROCK DRILL BIT Milton Vagins,Worthington, and Ralph Simon, Colum- The present invention relatesgenerally to improvements in the art of rock drilling and relates moreparticularly to the provision of an improved rock drill bit suitable foruse with either rotary or percussive drills and also par- I ticularlyadapted for rotary-percussive operation.

In the drilling of rock, the majority of operations presently employeither a percussive drill or a rotary drill dependent upon the types ofrock encountered. Normally, percussive drilling is employed for hardrock, such as granite, and for extremely abrasive softer rock, such assandstone; and rotary drilling is used on soft types of rock, such asshale. In the percussion method, apparatus is used which performsconstant percussion blows against the rock with the boring member or bitbeing backed off between blows and rotated or indexed slightly to a newstriking position. On the other hand, the rotary type employs apparatusin which a constant and uninterrupted rotation is'imparted to the bitwhich is retained under pressure and in constant contact with the rock.

While both the percussion drilling method and the rotary drilling methodhave been in widespreaduse for many years, neither of these modes candrill very hard rock types or extremely abrasive rock types at a highrate of penetration without the application of high power inputsandlarge applied thrust wihch, in turn, results in added down time dueto drill-steel failure and excessive bit wear. Furthermore, sincespecialized drilling machinery is required for each type of drillingwith vastly different bits being used in each instance, the investmentin equipment necessary in order to operate satisfactorily under varyingconditions a well as the costs resulting from down time for changingdrills are undesirably high.

Accordingly, in fairly recent years, it has been proposed to combine thepercussion method of drilling with the rotary method. This type ofdrilling operation is commonly referred to as a rotary-percussionmethod, and in exploiting the same, the drilling tool or bit is rotatedconstantly with sufficient thrust applied so that the mode of action ofthe bit cutting edges, charcteristic of rotary drilling is attained,while being simultaneously subjected to a constant series of percussionblows.

only limited success due to the fact that the drilling rnachines havebeen relatively'large and cumbersome and therefore incapable ofoperations in restricted areas. Furthermore, conventional bits of thetype used in rotary drilling as Well as those used with ordinarypercussion apparatus have not proven adaptable for combined rotaryapercussion operations, and the redesigned bits heretofore However, therotar y-percussion method of drilling has thus far enjoyed proposed forrotary-percussive drilling have likewise not been entirely satisfactory.

For example the bit shown and described in United States Patent No.2,294,004, dated August 25, 1942, is of one-piece construction withthe'wings. formed integral with the body and radiating outwardly fromthe apex of the head' along spiral or helical paths which virtuallypreeludes the use of wear resistant cutting inserts as .a practicalmatter due to the complicated, if not impossible, machining operationwhich would be necessitated. Thus, in order that the one-piece bits ofPatent No. 2,294,004 have any wear resistance whatsoever to the impactsresulting from rotary-percussive drilling, they must be formedspecification wherein like reference characters designate Patented Dec.29, 1964 ice in their entireties of selected metals specially treatedand machined at relatively high and prohibitive cost.

Another type of bit heretofore proposed for rotary-percussion operationi shown and described in United States Patent No. 2,507,221, dated May9, 1950, wherein the cutting wing or contact edge is formed separatelyof the body of a wear resistant material and in which flushing holes areprovided in the head. However, the symmetrical angles of the cuttingelements of this type of bit on opposite sides of their apices haveproven inefficient for rotary-percussive drilling, and the sharpterminal portions of the wings have been found to deteriorate rapidlyclue to extreme impact forces in these areas. Furthermore, the placementof the flushing holes inrelation to the cutting inserts is relativelyineffectual in cooling the inserts, and these bits have therefore notproven entirely satisfactory for combined rotary-percussion drilling.

United States Patent No. 2,756,967, dated July 31, 1956, shows anddescribes another type of rotary-percussion drill bit which recognizessome of the shortcomings of the prior tools, and this bit has enjoyed afair degree-of success. in. sharp angular corners at the periphery ofthe head, and since the greatest rates of bit wear occur near the outergage of the bit due to the fact that the amount of rock broken out perunit length of bit edge increases in proportion to the radial distancefrom the axis of rotation, these corne-r'portions are subjected to thegreatest force and friction in use and consequently cause a shortenedwear life. Also, the relatively sharp angularity of the mating portionsof adjacent surfaces of the head of this prior bit have been found tocreate fatigue points, and the means for cooling the cutting elementsstill leaves something to be desired. f

It is therefore an object-of the present invention to provide animproved bitfor rotary-percussion drilling which. obviates thedisadvantages and objections attendant prior tools intended for similaruse,

Another object of this invention is to provide a rotary- L percussiondrill bit which has a cutting head of hemispheroidal shape and whereinthe. cutting elements or wings are curved in'a plane which includes theaxis of the bit so as to increase the length of cutting edge per unitincrease in radial distance fromthe axis of rotation to equalize theamount of rock broken by all portions of the cutting edge per unitdistance advanceof the drill and tending to equalize the wear of thecutting edges over, their entire lengths, thus-resulting in maximumoperating efiicien'cy and long life. i z- Still another object of theinvention is to provide an improved bit of the rotary-percussion typewhich hasa body and cutting edges so designed as to eliminate sharpfatigue points and points of stress concentration, and

' These and other objects and advantages of the invention apparent fromthe following detailed descripf- 1 will become tion.

A clear conception of the construction'of a typical rotary-percussiondrill bit embodying the improvements constituting the present inventionmay be had by referring to' the drawings accompanying and forming apartofthis the same or similar parts in the several views. r

However, the wings of this hit again terminate FIG. -1 is asideelevation of a typical embodiment of removable drill bit body;

FIG. 2 is a fragmentary side elevation taken from an- 7 7 other side ofthe same drill bit;"

Y along the line 7 '7 of FIG. 1;

FIG. 8 is a transverse section taken along the line S8 of FIG. 1;

FIG- 9' is a transverse section taken along the line 9+9 of FIG. 1;

FIG. 10 is a similar section taken along the line 10- -10 of FIG. 1.; I

FIG.'11' is another transverse section taken along the line 11 -11 ofFIG. 1; and i and theplacement and formation of these holes 27 isextremely important inprolonging the life of the bits and their cuttingelements. To form the flushing holes 27, conduits 28 are punched in thehead 17 during fabrication thereof, such conduits 28 extending throughthe head from the inner end of the tapered socket 21' to the exterior ofthe. head at an inclined angle relative to the bit axis as shown in FIG.4." T he {angles 29 at which the conduits should'preferably be formedwith 'respect to the bit axis approximate twenty-eight to thirtydegrees, and thus, form openings 27 in the head which; are of oblongshape in the direction of the bit axis so'as to closely follow thecurvature of the extending wear portions 23of the cutting elements 19.

To augment the cooling effect and chip: clearance ob- 'tained by properformation and placement of the flushing FIG. 12 is an end view of 'asomewhat modified drill bit 5 embodying the invention butprovided' withthree blades or wings; 1 7

While the invention has been shown'and described herein as beingespecially applicable to a rotary-percus sion drill bit havinga taperedshank portion and formed.

in a particular manner of certain specified materials, it is notintended ordesired to thus unnecessarily limit the scope or utility ofthe. improvements by reason of such restricted embodiments; anditis'alsocontemplated that certain specific terminology used herein shall begiven the -j broadest .possible interpretation: consistent with thedisclosure. I Referring to FIGS. 1 to 11. of the drawings, theimprovedrotary-percussion rock drill bit. shown therein as; embodying theinvention comprisesin general, a unitary body 15 having a shank portion16 terminating atone end: in a hemispheroidal .head 17 provided withat'l'east one groove 18" traversing the head'frorn-the .bit apex to:

the region of the greatest circumference of the head,"a'nd at least onecutting element or insert 19 secured within "the groove 18 in asuitable-manner, as by soldering,fbrazing or welding, so that thecutting elements each'fhave an impact portion 23 extending from theirrespective. grooves.

The shanlc16. isz formed with a tapered socket'21 forte- 'ception by thedrill wa er, a drilling machine; but other means forattach'ment ofthebit .to the drill rod may be utilized.

"The-drill bitbody 15 rnay be forged in a customary 1 manner, and thecurved cutting elements which, areall .identical mayfbe fabricated of amaterial having great impact'strength such as tungsten carbide havingarela I tivelylar'ge. cobalt content. As shown, the cutting elements. 19are: curved in: the plane .which includ'es the axis,

of the head 17 on the rake angle side of each of the adjajcent cuttingelements. Thus, the placement of the flush ing holes 2'7 coupledwith thespiral formation of the chipways or recesses3linsures turbulent air flowin the.

' vicinity of the cutting edges 23 of the inserts 19. by inducing aspiral flow pattern and forcing the flushing fluid into a turbulentvortex, around the cutting edges. The unsymmetrical placement of the fflushing holes 27 so that they:

are. closer to the rake anglefside of, the adjacent cutting element alsohelps create the turbulent vortex of fluid flow and consequent reductionin hit edge temperatures during cutting operations, and this enhancementof the heat transfer pattern is extremely important to long bit life.The placement of the flushing holes and the patterning of the recesses31 is illustrated most vividly in FIGS. 7 to 11.

inclusive which reflect the shape of. the bit head along varioustransverse areas thereof. V a

While the improvements have been shown and 'described with specificreference to a two-bladed bit, they 7 may be utilized with similaradvantages in bits which have more than two cutting blades or wings, andFIG. 12 illustrates a three-bladed bit of the: present improved design.

Again, in the three-bladed construction, the head 37 of the bit isprovided with equally spaced grooves 38. traversing the head from theapex thereof to the region of its greatest circumference in planeslyingparall'el with.

the bit axis; and a cutting element 39 formed of a material possessinghigh impact strength :is'suitably secured,

'as'by'brazing, soldering or fwelding, within each of the. grooves 38';-Each of the: cutting elements 39 has. a wear surface or cutting edge 43extending outwardly from the of the bit and thejlongitudinal planeswithin which the cutting edges lie' throughoutthe lengthv thereofi'areall parallel to the axis of the bit. The groove 18 for receivingf thecutting elements 19 may conveniently beid'esigned so that the cuttingelements maybe of segmental shape approximating a quadrantof acircle asshown in FIG. 5', and the arciiately curved cutting'edges 23'ofeachofthe cutting elements 19 should preferably be formedwith a negativerake angle 24% of. between twenty and thirty degrees andjwitll areliefangle 25 of! approximately thirty.

degrees, these angleshaving heen found to afiord 'the pi'mostsatisfactory drilling and strength requirements.

to a fatigue condition resulting in the shorteningof the. 1

Also, the bit must not have any abrupt changes in cross section. in theimmediateflyicinity of the cutting edges I since such abrupt changesinthe configuration tend to lead drillinglife ofthe bit.

Tbe bit body isalso provided with flushing holes equal in number to thenumber of cutting elements 1 9 hemispheroidal head, and each :of thesewear surfaces, is

curved inthe plane whichl includes the axis Of the bitso as to followthe contour ofthehead. Also, the three,-

bladed head shown in FIG. -12 is provided with a plurality of flushingholes 47 formed. in a manner-similar'to that; 7 described with respectto the two-bladed head, and each ofth'ese holes 47 is placed adjacent tothe. rake angle. side.

44 of a cutting element 39. Again, a turbulent. flow of the flushingfluidin a spiral pattern mayxbe induced by forming the head 35"withspiral or helical recesses 51.

extending from' each of the flushing holes 47 to the apex of the headatthe rake angle side ofthe adjacent cutting element. 7

"The improved drill; bits have been subjected to extensive tests, andthe results ofthese tests have beenyex- 'tremcly satisfactory and haveindicated that extremely efiicient drilling-is accomplished with thelife of the bits being prolonged toa considerable extent. The bits wereIn addition, each of. the .flushing holes 27" should be placed as closeas possible to the rake angle found to start their holes with ease andwith very little tendency to walk away or slip from their initialstarting positions. Furthermore, the bits have been shown to runremarkably cool and drill at an excellent rate of penetration. Noflushing difiiculties have been encoun tered with these bits even whendrilling at a rapid rate, and rock removal is accomplished easilywithout evidence of choking.

While the bits illustrated herein have the wings thereof formed as apair of special carbide steel inserts possessing high impact strengthand secured as by soldering or brazing within grooves formed in thehemispheroidal head, these wings 19, 39 may be formed integral with thehead which may then be specially treated to increase the impact strengththereof. Also, in bits having only one pair of wings as in FIGS. 1 to llinclusive, the wings may either be formed of two separate end abuttingsegmental inserts, as shown, or a single semi-circular insert may beused, and in either case, the continuous nature of the oppositelydirected end-abutting or one-piece wings imparts strength and rigidityto the bit since the shocks are more equally disbursed across the wingsin operation and torque is more effectively absorbed. In addition, bytapering the wings at their abutting portions or at the bit apex as at32-, the life of the inserts or cutting elements may be prolonged sincethe effectiveness of the turbulent vortex formed by the flushing ports27 and recesses 31 which terminate at the apex is enhanced. It shouldalso be understood that additional flushing holes may be provided iffound desirable, and the bits shown and described may be usedetfectively either with a drilling system wherein cuttings are removedfrom the hole by means of vacuum drawn through the bit and drill steelor by pressure projected through the steel and the bit.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

We claim:

1. A rotary-percussion rock drill bit comprising, a unitary body havinga shank portion terminating at one end in a hemispheroidal head providedwith at least two equally spaced wings formed with cutting edgesextending outwardly from said head and traversing the head from the apexthereof to the region of its greatest circumference in longitudinalplanes which lie parallel with the bit axis, said wings each beingcurved in the plane which includes the axis of the bit so as to followthe contour of the head and being tapered inwardly from their outercutting edges toward each other and towardthe apex of said head.

2. A rotary-percussion rock drill bit according to claim 1, wherein thecutting edges of said wings each have a negative rake angle of fromtwenty degrees to thirty degrees and a relief angle of approximatelythirty degrees.

3. A rotary-percussion rock drill bit according to claim 1, wherein thecutting edges of said wings each have a rake angle side and a reliefangle side, and the body is formed with conduits providing fluidflushing holes extending therethrough to the exterior of the head andequal in number to the number of wings, each of said flushing holesterminating closer to the rake angle side than the relief angle side ofa wing, and the head being formed with outwardly open recesses extendingfrom each of said flushing holes to the apex of said head adjacent thetapered portions of the wings.

4. A rotary-percussion rock drill bit according to claim 3, wherein theconduits formed in the body are inclined relative to the bit axiswhereby the terminal portions of the flushing holes form openings in thehead which are of oblong shape and closely follow the curvature of theadjacent wings.

5. A rotary-percussion rock drill bit according to claim 3, wherein therecesses formed in the head extend along an approximately spiral path onthe rake angle side of the adjacent Wing from the terminal end of eachof the flushing holes to the apex of the head.

6. A rotary-percussion rock drill bit comprising a unitary body having ashank portion terminating at one end in a hemispheroidal head providedwith a groove diametrically traversing the head from the apex thereof tothe region of its greatest circumference in a plane lying parallel withthe bit axis, and a pair of end-abutting cutting elements formed of amaterial possessing high impact strength secured within said groove andhaving impact portions extending from the groove to provide oppositelydirected wings having outer cutting edges and each curved in the planewhich includes the axis of the bit so as to follow the contour of thehead, the abutting ends of said cutting elements being tapered towardeach other and toward the apex of said head to provide a transverserecess.

References Cited by the Examiner UNITED STATES PATENTS 2,009,742 7/ 35Mitchell l329 2,119,349 5/38 Pearce -393 2,578,593 12/51 Phipps 1754l0 X2,756,967 7/56 Meutsch 175410 2,973,047 2/61 Edgar 175--4l9 X 7 FOREIGNPATENTS 464,654 l/ 14 France.

CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN BENDETT, Examinen' V

6. A ROTARY-PERCUSSION ROCK DRILL BIT COMPRISING A UNITARY BODY HAVING ASHANK PORTION TERMINATING AT ONE END IN A HEMISPHEROIDAL HEAD PROVIDEDWITH A GROOVE DIAMETRICALLY TRAVERSING THE HEAD FROM THE APEX THEREOF TOTHE REGION OF ITS GREATEST CIRCUMFERENCE IN A PLANE LYING PARALLEL WITHTHE BIT AXIS, AND A PAIR OF END-ABUTTING CUTTING ELEMENTS FORMED OF AMATERIAL POSSESSING HIGH IMPACT STRENGTH SECURED WITHIN SAID GROOVE ANDHAVING IMPACT PORTIONS EXTENDING FROM THE GROOVE TO PROVIDE OPPOSITELYDIRECTED WINGS HAVING OUTER CUTTING EDGES AND EACH CURVED IN THE PLANEWHICH INCLUDES THE AXIS OF THE BIT SO AS TO FOLLOW THE CONTOUR OF THEHEAD, THE ABUTTING ENDS OF SAID CUTTING ELEMENTS BEING TAPERED TOWARDEACH OTHER AND TOWARD THE APEX OF SAID HEAD TO PROVIDE A TRANSVERSERECESS.